Manicouagan
Key facts
- Country
- Canada
- Diameter
- 100 km
- Age
- about 214 million years
- Location
- 51.38° N, 68.70° W
A striking ring-shaped reservoir about 70 km across surrounding René-Levasseur Island, one of the most recognisable impact structures when seen from space.
Seen from orbit, Manicouagan looks like a giant eye staring up from the forests of Quebec. A ring of water about 70 km across encircles a large island, making it one of the most photographed craters on Earth. It is sometimes called the Eye of Quebec.
The impact. About 214 million years ago, in the Late Triassic period when early dinosaurs were spreading across the supercontinent Pangaea, an asteroid perhaps 5 km across struck here. The original crater is thought to have been about 100 km wide. It has since been worn down by erosion, including scouring by ice-age glaciers, which removed the rim and much of the surrounding rock.
A ring made of water. The famous ring is not the crater rim. Erosion picked out a circular zone of weaker rock around the crater's centre, and over time a ring of lakes formed there. In the 1960s the Daniel-Johnson Dam was built on the Manicouagan River to generate hydroelectric power, and the rising water joined the lakes into a single annular reservoir. The island in the middle, René-Levasseur Island, is the remains of the crater's central uplift and a thick sheet of impact melt rock. Its highest point, Mont Babel, rises to nearly 1,000 m above sea level.
The melt sheet. One of Manicouagan's great scientific gifts is its impact melt sheet, a layer of rock that was completely melted by the impact and then cooled. It is up to a few hundred metres thick and is well exposed on the island. Because the melt formed at a single moment, it is ideal for precise dating, and studies of it have helped scientists understand how melt sheets behave in large craters on the Moon and other planets.
An extinction suspect cleared. Manicouagan was once suggested as a cause of the mass extinction at the end of the Triassic period. Precise dating showed that the crater is about 13 million years older than that extinction, which happened around 201 million years ago. Scientists also once proposed that Manicouagan was part of a chain of craters formed by a single broken-up object, but more recent dating has shown the other craters in that proposal formed at different times.
Visiting. The reservoir lies in remote boreal forest north of Baie-Comeau. A road, Route 389, passes close to its eastern side. Most people know Manicouagan from photographs taken by astronauts, who often single it out as one of the most beautiful sights from orbit.
Did you know?
The ring-shaped lake was enlarged into a single reservoir by a hydroelectric dam built in the 1960s.
Astronauts often photograph Manicouagan because it is so easy to spot from orbit.
René-Levasseur Island covers about 2,000 square kilometres, making it one of the largest lake islands in the world.